Global Positioning System generally involves a system for determining a position on the Earth's surface by comparing radio signals from several satellites. The system essentially comprises 24 satellites equipped with radio transmitters and atomic clocks. Depending on a geographic location, a GPS receiver samples data from the satellites and calculates the time for each satellite signal to reach the GPS receiver. From the difference in time of reception, the location may be determined. The GPS generally represents a constellation of 24 satellites that orbit the Earth where ground receivers are able to pinpoint a precise geographic location. The location accuracy may range from anywhere from 10 to 100 meters.
The GPS is owned and operated by the United States Department of Defense but is available for general use around the world. Twenty one GPS satellites and three spare satellites are in orbit above the Earth. The satellites are spaced so that from any point on Earth, four satellites will be above the horizon. Each satellite contains a computer, an atomic clock and a radio. With an understanding of its own orbit and the clock, each satellite continually broadcasts its changing position and time. Periodically (e.g., daily), each satellite will checks its own time and position with a ground station and makes any minor correction, if necessary. On the ground, any GPS receiver may contain a computer that triangulates its own position from information provided by a plurality of satellites (e.g., three to four satellites). The result is provided in the form of a geographic position (e.g., longitude and latitude). If the receiver is also equipped with a display screen that shows the map, the position can be shown on the map. In addition, an altitude reading may also be provided.
There are many instances where the GPS satellite signal may be interfered with or otherwise compromised. Generally, the user will experience a delay, difficulty in receiving a reading or data that is incorrect or misleading. The user is essentially unaware of the cause, an amount of interference or even the presence of interference. For example, the user may be completely unaware that the signal is being interfered with and may rely on delayed signals or inaccurate data. Therefore, as the user is unaware of interference detection, the user does not have the information to compensate for the interference.
In view of the foregoing, it would be desirable to provide a technique for detecting GPS interference which overcomes the above-described inadequacies and shortcomings.